1. Field of the Invention
The present invention relates to an optical pickup device which writes and/or reads information to and/or from an optical disc or magneto-optical disc.
2. Description of Related Art
Various optical pickup devices have been proposed and widely used to write and/or read information to and/or from an optical disc, for example. An optical pickup device of this kind comprises an optical block including an objective lens to focus a laser light on a signal recording area of an optical disc, an objective lens drive to move the objective lens in a focusing direction parallel to the optical axis of the objective lens and a tracking direction orthogonal to the optical disc of the objective lens, and a sliding base to support the optical block and objective lens drive thereon.
The optical block includes a light source to emit a laser light, the objective lens to focus the laser light onto the signal recording area of the optical disc, a photodetector to detect a return light from the signal recording area of the optical disc, various lenses, etc. The objective lens drive comprises a lens holder to hold the objective lens, a supporting base to support the lens holder movably in the focusing and tracking directions, and a biaxial actuator to move the lens holder in the focusing and tracking directions.
The sliding base is supported movably on first and second guide shafts disposed in parallel to each other, and moved radially of the optical disc by means of a sliding base driving mechanism. The sliding base includes a mount plate on which the optical block and objective lens drive are installed, first and second bearings supported on the first guide shaft, and a third bearing supported on the second guide shaft.
In the optical pickup device constructed as in the above, as the sliding base is moved on and along the first and second guide shafts, the objective lens is moved radially of the optical disc to a position corresponding to a desired recording track on the optical disc. Further in this optical pickup device, the objective lens drive moves the objective lens in the focusing and tracking directions, the laser light irradiated through the objective lens via the optical block is focused on the signal recording area of the optical disc, and a return light from the signal recording area is detected to read information written on the optical disc.
However, the conventional optical pickup is disadvantageous in that when information is read from an optical disc, the sliding base itself is moved and the objective lens drive and optical disc spinning drive mechanism in operation are mechanically vibrated, thus causing the sliding base to resonate with the mechanical vibration.
To suppress such vibration in the conventional optical pickup device, a massive piece is disposed in a predetermined position on the sliding base to shift the resonance frequency band or reduce the amplitude of the vibration.
However, the provision of the massive piece adds to the number of parts in the conventional pickup device, the material and manufacturing costs, the total weight of the optical pickup device, and also to the structural limitation which will make it difficult to freely design an optical pickup device.
The Japanese Published Unexamined Patent Application No. 9-180201 discloses an optical pickup device using a sliding base improved to cope with the above-mentioned vibration problem. FIG. 1 is a plan view of this conventional optical pickup device. As shown, the optical pickup device includes a sliding base 105 supporting an optical block 103 and objective lens drive 104 thereon. The sliding base 105 is provided with a first bearing 111 and a second bearing 112, both supporting together a first guide shaft 101, and a third bearing 113 supporting a second guide shaft 102.
In the sliding base 105, the third bearing 113 has a fulcrum P13 thereof positioned to define an isosceles triangle together with a fulcrum P11 of the first bearing 111 and a fulcrum P12 of the second bearing, with a segment connecting the fulcrums P11 and P12 taken as the base of the isosceles triangle, in order to suppress the above-mentioned vibration. Further, the sliding base 105 supporting the optical block 103 and objective lens drive 104 thereon has a center of gravity thereof positioned on the bisector orthogonal to the base of the isosceles triangle to further reduce the vibration.
However, if the center of gravity of the sliding block 105 is located outside the triangle defined by the fulcrums P11, P12 and P13 of the first, second and third bearings 111, 112 and 113, respectively, the vibration cannot be reduced effectively or it will increase since the triangle is an isosceles one.
The resonance characteristic of the conventional optical pickup device in FIG. 1 is shown in FIG. 2 in which the horizontal axis indicates a resonance frequency and the vertical axis indicates an output intensity. As seen from FIG. 2, output peaks are included within a band ranging from 1,000 to 4000 Hz, which is not advantageous for the optical pickup device.
According, the present invention has an object to overcome the above-mentioned drawbacks of the prior art by providing an optical pickup device capable of suppressing the resonance taking place in a sliding base thereof
The above object can be achieved by providing an optical pickup device comprising, according to the present invention:
an optical system including an objective lens;
an objective lens drive including a holder to support the objective lens, a member to support the lens holder movably in a first direction parallel to the optical axis of the objective lens and a second direction perpendicular to the optical axis of the objective lens, and means for driving to move the lens holder in the first and second directions; and
a sliding base to support the optical system and objective lens drive.
The sliding base is supported over first and second guide shafts disposed in parallel to each other, and has a plurality of main bearings supported on the first guide shaft and an auxiliary bearing supported on the second guide shaft.
The auxiliary bearing is disposed to have a fulcrum thereof positioned on a straight line connecting a middle point of a segment connecting fulcrums of the plurality of main bearings positioned at opposite axial ends of the first guide shaft, and the center of gravity of the sliding base supporting the optical system and objective lens drive thereon.
In the optical pickup device as constructed as in the foregoing, the middle point of the segment connecting the fulcrums of the plurality of main bearings positioned at opposite axial ends of the first guide shaft, is positioned on the center of gravity of the sliding base supporting the optical system and objective lens drive thereon, so that the sliding base can be inhibited from resonating. It should be noted that the fulcrums and center of gravity refer to projected points on a same plane for the simplicity of illustration and explanation.
These objects and other objects, features and advantages of the present intention will become more apparent from the following detailed description of the preferred embodiment of the optical pickup device according to the present invention when taken in conjunction with the accompanying drawings.